1. Field of the Invention
The present invention relates to a circuit for generating reference current, and more particularly, to a circuit for generating reference current for providing a band gap reference (BGR) current and a proportional to absolute temperature (PTAT) current using a single external pad.
2. Background of the Related Art
In general, a circuit for generating reference current for providing a constant current having a predetermined level is widely used in a bias circuit or an active load of an analog integrated circuit or an RF integrated circuit. Particularly, most analog integrated circuits use a bias mode based on the circuit for generating reference current. The circuit for generating reference current provides a band gap reference (BGR) current which can supply a constant current irrespective of a fabricating process or a surrounding temperature variation, and a proportional to absolute temperature (PTAT) current which can supply a current linearly proportional to absolute temperature.
FIG. 1 illustrates a conventional circuit for generating reference current 1. Referring to FIG. 1, the conventional circuit for generating reference current 1 generates a BGR current IBGR and a PTAT current IPTAT using two external pads P1 and P2 and two external resistors RBGR and RPTAT and provides them to an analog integrated circuit or an RF integrated circuit 2 as a reference current.
With the rapid development of information communications, an analog integrated circuit or an RF integrated circuit is required to operate at a high speed. Thus, techniques of manufacturing the analog integrated circuit or RF integrated circuit are being developed such that the integration, reliability and response speed of the analog integrated circuit or RF integrated circuit are improved. The increased integration of the analog integrated circuit or RF integrated circuit reduces its package size. To reduce the package size of the analog integrated circuit or RF integrated circuit requires a decrease in the number of external pads.